The present invention relates to an image processing system. The image processing system of the present invention is especially suitable for use in an apparatus which receives two different video signals, for example, two different video signals from a magnetic recording/reproducing apparatus such as a video tape recorder and a signal source such as a television tuner, compresses one of the two video signals on the time axis, merges the compressed video signal into the other video signal, and supplies the resultant signal to a Braun tube in a television set so that two-field images are displayed simultaneously on the Braun tube.
Such a system which simultaneously displays two different video signals on one Braun tube, is well known and is called a "picture-in-picture system".
A conventional apparatus using the above-described system is provided with, two memories for storing one of two different video signals to be displayed in a sub-field (small area) on the Braun tube. The video signal is written sequentially into the memories and at the same time the signal is read out from the memories in a compressed form. The retrieved signal is merged into the other video signal to be displayed in a main-field (large area) on the Braun tube. Writing and reading of the two memories are switched at the input and output stages of the memories in synchronism with the two video signals. Namely, writing into the memories is in synchronism with the sub-field video signal, while reading from the memories is in synchronism with the main-field video signal.
However, in the above-mentioned system with the ability of simultaneous reading and writing of the memories, the main-field and sub-field video signals are usually out of phase with each other, and therefore the memory contents are replaced with the next field information in the course of monitoring for the sub-field, with the result that different images are displayed on the upper and lower portions of the sub-field. This problem can be solved by the provision of three memories which are sequentially written and read the sub-field video signal.
But, the system having a plurality of memories, with their input and output being switched for reading and writing, requires a complex input/output control system and therefore it is rendered expensive.